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  • many of the tragic events in Japan.

  • In the news we've we've seen and heard this new term Millie Seaver.

  • It sort of used it as a unit of radiation, eh?

  • So what is it?

  • So we got our Millis Eve it unit.

  • And of course, not surprisingly amily.

  • Seaver.

  • It is one thousands off 11 secret, of course.

  • But what is this Eve it receive?

  • It is, if you like the human response, That's the important thing.

  • Is the human response to to radiation It contains all the information it needs about the type of radiation on the type of tissue.

  • In other words, where the radiation ends up with the physics of the of the measurement, in a sense, comes from our unit of Grey, Our unit of of Dose Andi.

  • The united ace is measured in one jewel per kilogram.

  • In other words, the energy that's deposited in literally one kilogram of tissue, which is probably around about that size.

  • To humanize the response, we clearly need to know about the effect of the radiation.

  • So the first thing to do is to multiply the dose in gray by a radiation factor on DDE.

  • If they're out of particles, particularly destructive.

  • We reallocate the factor of about 20 for gamma only a multiplier of one, because we know that an Alfa source is more damaging than the gamma source.

  • Actually, most of the gamma goes through you without being absorbed.

  • So it's whereas the alfa particles are going to get stopped very easily by your by your tissue.

  • That's liberating their energy.

  • We want our measurement deceiver to reflect how dangerous these thes particles are in some relative way.

  • So a doubt a particle is 20 times more dangerous than a gamma photons.

  • Clearly, we want to know where what sort of particulate waas, but we also need to know where it lands up now.

  • Radiation deposited in certain types of tissue, like Gonen, is the breast of thyroid and so on, and more likely to have a negative response on other words of development of cancer than than bone or something like that.

  • So we have to allocate different portion different Waiting's two different different tissues to reflect their likelihood of responding to radiation.

  • So we then multiply our Cleveland dose by another parameter, which gives us the effective equivalent dose on Here we are we've actually arrived at our arse.

  • Evert.

  • Our measurement notice.

  • It's still got the same fundamental unit joules per kilogram.

  • What does one Seaver it actually actually do to us?

  • Well, the one see vert given over a lifetime.

  • In other words, we add up our annual dose over many years or our little individual doses.

  • One Seaver would give us around about 5% chance of suffering from a fatal cancer.

  • So in other words, now we've We have humanized the unit into a probability when I say stress that it is only a probability of getting getting a fatal cancer.

  • Okay, so let's try and put this in some sort of some sort of context.

  • What?

  • You know what the quantity is actually a Seaver on.

  • The easiest way to do that is to just to think about our natural radiation dose.

  • In other words, the dose that comes from, um, gamma rays coming out of the rocks.

  • Very small cosmic rays coming out of coming out of the sky again.

  • Very small.

  • Actually.

  • The carbon on the potassium inside us also gives us our own gamma radiation.

  • And so if we had all these things together on DDE.

  • Assuming a sort of average UK type of figure, we end up with about 2.5 mil e c verts as the annual average dose for somebody in the UK Now, of course, you can see that you're likely to live long enough to actually receive receiver to radiation.

  • Unless, of course, you have a medical X ray or ah, lot of dental X rays, you would not be able to get Thio receiver.

  • So, really, the units of Seaver it are only really relevant for nuclear industry.

  • Clearly, the nuclear reactor that's gone wrong will generate a lot of radioactive material.

  • Certainly if it gets out into the environment with cesium.

  • For instance, of Gamma remit, I, Dean and sauna beater emitter on dhe thes could be taken up and in the body.

  • It could be breathed in and so on, and that will produce over a lifetime, quite a high dose or could produce quite a high dose.

  • So it's right that people are removed from the from the locality unless they're wearing protective protective equipment on taking appropriate appropriate precautions and so on.

  • Seaver.

  • It is really designed in terms of the units and probabilities as to to try and work out what lifetime doses do.

  • A long term doses lily with a very sudden and short days.

  • Then anything can happen.

  • In point of fact, if you get to the sort of level of 5 to 10 see votes in total, then we'll fight to 10 grey.

  • That is a sort of radiation dose that would make you seriously ill.

  • Onda Very unlikely to survive Still a scientific unit.

  • But in the end, we've got a certain uncertainty in the fact that somebody having a certain level of radiation one person is going thio get developed cancer.

  • One person, isn't it?

  • It's really the probability that that particle or that gamma photons actually did some damage to our d.

  • N A motor didn't go straight past that having any effect whatsoever.

  • But some of them will obviously cause damage.

  • On, of course, is a probability that that damage will actually go on to develop cancer.

  • And that's actually very, very low number.

  • Well, I thought I'd just go and show you a brief demonstration of how to measure how we measure gamma radiation.

  • You may have seen that garden mullah tubes and the little and counters that they were using to measure Seaver since Arnold Equivalent in camera.

  • So I'd like to just show you that Well, clearly, with radiation sources being very dangerous, we have to keep them under lock and key is gonna cover it.

  • And inside this box, you see right in the center of that, that box is a tiny dot and that's a cesium 137 that's producing radiation all the time.

  • Now it's in this box such that it's safe for me to handle.

  • Way got here is a is a gamma detector is going to detect the gamma radiation from the from the cesium.

  • It's a special crystal inside the sea inside, too.

  • Can there?

  • This is very similar device to the thing that people have been using.

  • Toe monitor, monitor radiation.

  • You might have seen people doing this.

  • This is this is a sort of instrument that they would have been using.

  • Okay, so what you're now seeing is the gamma particles being received on being counted.

  • Well, each one of those gamma photons is carrying a certain amount of send amount of energy.

  • And of course, we can adult that energy.

  • Assuming that it all ends up in one kilogram of tissue, then we can calculate the dose on dhe.

  • Therefore, the effective dose in Seaver's.

  • So effectively we've we've now counted the number of gamma particles that arriving at our detector.

  • Now, of course, what we don't know is where all the other particles were going in that cesium sample.

  • Because, of course, they're going in all directions.

  • So again we got we got to know something about the geometry of where the where the season particle is.

  • And so if it was on the skin, for instance, then clearly that's going to most of that.

  • Half of it is going to go into the skin.

  • If it's in the air somewhere, then clearly the gamma rays are going to go in all directions.

  • I'm only going to get a small part of that.

  • Well, what we got here is yet another method of measuring radiation somewhat simpler than the radiation method.

  • We've just seen the gamma counter, but this is sensitive to Alfa beater on gamma.

  • So if I then pick up in amorous IAM source, which is contained in this in this little container was in this little container, then I place it near my Geiger counter.

  • Then you see how close I have to get before this actually registers any sort of can on.

  • Really?

  • That shows us that the alpha particles coming out of here don't come.

  • Don't travel very far in there.

  • No effect there, really.

  • Lots of this.

  • The sort of radiation sources which we're allowed to use in teaching laboratories by their very nature are going to be very low levels off radiation.

  • They're enough to us to measure, but hopefully not enough for us to do any serious, serious damage with.

  • So this is this is off the scale in terms of microsieverts on it would have to stay there on my skin, for instance, for for quite some time before I got anywhere near a dangerous level.

many of the tragic events in Japan.

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